The Great Attractor is a gravity anomaly in intergalactic space within the range of the
Hydra-Centaurus Supercluster that reveals the existence of a localized concentration
of mass tens of thousands times that of the Milky Way. This mass is observable by its
effect on the motion of galaxies and their associated clusters over a region hundreds
of millions of light-years across. These galaxies are all redshifted, in accordance
with the Hubble Flow, indicating that they are receding relative to us and to each other,
but the variations in their redshift are sufficient to reveal the existence of the anomaly. The
variations in their redshifts are known as peculiar velocities, and cover a range from
about +700 km/s to −700 km/s, depending on the angular deviation from the direction
to the Great Attractor.
Location The first indications of a deviation from
uniform expansion of the universe were reported in 1973 and again in 1978. The location of
the Great Attractor was finally determined in 1986, and is situated at a distance of
somewhere between 150 and 250 Mly from the Milky Way, in the direction of the constellations
Triangulum Australe and Norma. While objects in that direction lie in the Zone of Avoidance
and are thus difficult to study with visible wavelengths, X-ray observations have revealed
that the region of space is dominated by the Norma cluster, a massive cluster of galaxies
containing a preponderance of large, old galaxies, many of which are colliding with their neighbours,
and/or radiating large amounts of radio waves. Debate over apparent mass
In 1992, much of the apparent signal of the Great Attractor was attributed to the effect
of Malmquist Bias. In 2005, astronomers conducting an X-ray survey of part of the sky known as
the Clusters in the Zone of Avoidance project reported that the Great Attractor was actually
only one tenth the mass that scientists had originally estimated. The survey also confirmed
earlier theories that the Milky Way galaxy is in fact being pulled towards a much more
massive cluster of galaxies near the Shapley Supercluster, which lies beyond the Great
Attractor. The dark flow
The dark flow is a purported velocity tendency of galaxies to move in a particular direction,
which was formerly thought to be caused by the Great Attractor, but then theorized to
be outside the observable universe. These findings were published in 2008 but were later
contradicted by data from the Planck satellite. In fiction
The Great Attractor is mentioned in the "Pip and Flinx" series by novelist Alan Dean Foster,
in the book Flinx's Folly. The Great Attractor is referenced as an attempt of an ancient
alien race to create something with enough gravitational pull to move the Milky Way,
among other galaxies. In the film Men in Black, the Great Attractor
is said to be both sentient and the cause of the 1977 New York City blackout, during
a practical joke. It is also a major plot point in the Xeelee
Sequence series of books by Stephen Baxter, specifically in the book Ring where it is
described as a cosmic string, artificially made into a loop creating the phenomenon of
the Great Attractor. In the Doctor Who novel The Quantum Archangel,
the Great Attractor is said to be the last creation of a cosmic super-race called the
Constructors of Destiny, and is a quantum supercomputer constructed of strange matter
with the event horizon as its memory store, designed for the purpose of understanding
the Universe. In the Discworld novel Reaper Man, the supreme
"Death", Azrael, is described as "the Great Attractor" among other titles and has an appropriately
large mass; the text states that a supernova would appear as a glint in his eye.
See also CfA2 Great Wall
Dark Matter Hercules–Corona Borealis Great Wall
Shapley Supercluster References
Further reading Dressler, Alan. Voyage to the Great Attractor:
Exploring Intergalactic Space. New York: Alfred A. Knopf. p. 355. ISBN 978-0-394-58899-5.
Videos Cosmography of the Local Universe at vimeo
showing Great Attractor. A film by Hélène Courtois, Daniel Pomarède, R. Brent Tully,
Yehuda Hoffman, and Denis Courtois.